This invention generally relates to electrical connectors, and more specifically to a box contact for mounting on a printed circuit board which eliminates wicking during wave soldering, and method of manufacturing the electrical contact.
Box contacts that have substantially box shaped upper contact portions and downwardly extending mounting legs intended to pass through openings or holes in printed circuit boards are well-known and extensively used and have for many applications. Such box contacts generally have relatively large interior spaces into which there typically project a plurality of spring contacts intended to resiliently engage a male contact member inserted into the box contact. However, prior art designs require manual masking in order to prevent the entry of solder into the lower openings of the box contacts during wave soldering. The entry of the solder through the bottom opening of the box contact and subsequent hardening of the solder have presented problems since the solder interferes with the full insertion of the male contact and, additionally, may interfere with and in some cases substantially eliminate the resilient properties of the spring fingers or contacts.
Referring to FIG. 1, a conventional box contact of the type under discussion is generally designated by the reference numeral 10. The contact has an upper portion 10a which generally has a rectangular substantially uniform cross-section defining an interior space 11 as shown. Spring contacts or fingers 10b extend into the interior space of the box contact 10. Mounting legs 10c depend from the upper box portion 10a, with a small portion 10d of the mounting legs protruding beyond the printed circuit board 12. The protruding portions 10d are the portions of the mounting legs generally soldered to the lands or soldering pads (not shown) on the lower surface of the printed circuit board. Shown in dashed outline and designated by the letter S is a peak of molten solder which propagates through a wave-soldering machine in waves, as is well-known to those skilled in the art. In order to prevent the solder from entering through the lower open end of the box connector, a plug P or other masking scheme is commonly used. After wave-soldering, the solder mask or the plugs have to be removed.
Referring to FIG. 2, Zierick Manufacturing Corporation, the assignee of the present application, developed a box contact to eliminate masking and plugging of the holes useful for some wave-soldering applications. By selecting relative dimensions shown in FIG. 2, wherein the box B above the printed circuit board has dimensions greater than the dimensions of the aperture or hole 14 in the printed circuit board. Only relatively small mounting legs 10c extend through the hole so as to provide minimal metal within the area of the printed circuit board hole. Tests show and production runs confirm that this design prevents solder wicking if a standard wave soldering machine is used. However, with the introduction of surface mount technology, there are new turbulent wave-soldering machines for which the design suggested in FIG. 2 is not adequate.
Circuit board sockets have been disclosed for addressing this problem. For example, in U.S. Pat. No. 3,864,004, a socket is disclosed which has an inner surface of the body solder-resistant to prevent solder from flooding into the socket. However, in order to prevent solder from flooding and remaining in the socket, a solder-resist is used, such as a resistant aluminum oxide coating. The patent also suggests other alternative solder resists, such as chrome plate and a number of other commercially available resists. However, the use of solder resists that must be plated or deposited on a selected surface entails additional steps in the manufacturing process and this complicates the manufacturing process and makes the terminals more costly to manufacture. A pin and socket connector assembly utilizing a similar solder resist approach is disclosed in U.S. Pat. No. 3,222,632, and a circular board eyelet also utilizing a solder resist layer is disclosed in U.S. Pat. No. 4,070,077.